Warning dealer to take part (5)
I believe the answer is:
alert
'warning' is the definition.
(I know that alert is a type of warning)
'dealer to take part' is the wordplay.
'take part' says the answer is hidden in the clue (I've seen 'taking part of' mean this).
'ALERT' can be found hidden inside 'dealer to'.
(Other definitions for alert that I've seen before include "Watchful, sharp" , "Vigilant, watchful" , "Watchful, quick-thinking" , "Lively" , "Signal danger" .)